I talked to shelby about it about a month ago...that part# will fit a gt, but requires cutting out the original black grille. They also have a kit that simply slides in place of the old grille(not listed on their website) that goes for $200 and some change.
probably pretty easy, but I just opted to go for the kit. I'd rather be able to put my stock grille back in if I want to change back. When I first talked to shelby about the grille about 6 months ago, they didn't even have instructions printed on how to do it. The price is still pretty reasonable if you look at other kits